Method for searching global maximum power point

Abstract

An exemplary method is disclosed for searching a global maximum power point in an arrangement comprising a series connection of photovoltaic power sources. The method can include determining a value of a reference by adding an increment to a previous value of the reference, wherein the value of the increment is determined on the basis of the power produced by the power sources.

1 . A method for searching a global maximum power point in an arrangement having a series connection of photovoltaic power sources, and means for controlling a first quantity of the series connection, wherein one of two series connection quantities which represent a voltage over the series connection and a current through the series connection is defined as the first quantity, and another of the two series connection quantities is defined as a second quantity, and wherein the method comprises:
 determining values for the first quantity and the second quantity;   determining a power (p) produced by the power sources;   setting the value of the first quantity as a first parameter, when the value of the determined power exceeds a highest found power (p MPP ), wherein the first parameter represents the value of the first quantity at the highest found power;   setting the determined power (p) as a new value of the highest found power, when the value of the determined power (p) exceeds a present value of the highest found power;   determining a value of a first quantity reference by adding an increment to a previous value of the first quantity reference, wherein a value of the increment is determined based on the highest found power;   controlling the first quantity based on the first quantity reference; and   setting the first parameter value as the global maximum power point, when the first quantity reference or the second quantity has reached a set limit.   
     
     
         2 . A method according to  claim 1 , wherein determining the value of the first quantity reference comprises:
 calculating a sum of the first quantity reference and a minimum increase;   calculating a second parameter by dividing the highest found power (p MPP ) by the second quantity and comparing the second parameter with the sum, provided the value of the determined power (p) does not exceed the highest found power (p MPP );   setting the second parameter as the first quantity reference, provided the value of the determined power (p) does not exceed the highest found power (p MPP ) and the second parameter is larger than the sum, otherwise setting the sum as the first quantity reference.   
     
     
         3 . A method according to  claim 1 , wherein a voltage (v) over the series connection of PV power sources represents the first quantity and a current (i) through the series connection represents the second quantity. 
     
     
         4 . A method according to  claim 1 , wherein current (i) through the series connection of PV power sources represents the first quantity and voltage (v) over the series connection represents the second quantity. 
     
     
         5 . A method according to  claim 1 , wherein, for at least a part of a time, current (i) through the series connection of PV power sources represents the first quantity and voltage (v) over the series connection represents the second quantity, and, for another part of the time, the voltage (v) over the series connection of PV power sources represents the first quantity and the current (i) through the series connection represents the second quantity. 
     
     
         6 . An apparatus for searching a global maximum power point of an arrangement having a series connection of photovoltaic (Pv) power sources, wherein one of two series connection quantities which represent a voltage over the series connection and a current through the series connection is defined as a first quantity, and another the two quantities is defined as a second quantity, the apparatus comprising:
 means for determining a power (p) produced by power sources;   means for determining a value of a first parameter based on a highest found power, wherein the first parameter represents a value of the first quantity at the highest found power;   means for determining a new value for the highest found power based on the determined power (p);   means for determining a value of a first quantity reference by adding an increment to a previous value of the first quantity reference, wherein the value of the increment is determined based on the highest found power; and   means for setting the first parameter value as a global maximum power point, when the first quantity reference or the second quantity has reached a set limit.   
     
     
         7 . An apparatus according to  claim 6 , comprising:
 means for controlling the first quantity based on the first quantity reference.   
     
     
         8 . An apparatus according to  claim 7 , comprising:
 means for estimating current (i) through PV power sources based on a current of an inverter on the grid side during operation, a voltage (e) produced by the inverter, and a voltage (v C ) over a capacitor connected in parallel with the PV power sources.   
     
     
         9 . An apparatus according to  claim 7 , wherein the means for controlling the first quantity is a PI controller comprising:
 a first feedforward term cancelling a DC component of determined power (p); and   a second feedforward term, wherein the second term is formed by a multiplication of the first quantity reference, a capacitance of a capacitor connected in parallel with the PV power sources, and a derivate of the first quantity reference.   
     
     
         10 . A method according to  claim 2 , wherein a voltage (v) over the series connection of PV power sources represents the first quantity and a current (i) through the series connection represents the second quantity. 
     
     
         11 . A method according to  claim 2 , wherein current (i) through the series connection of PV power sources represents the first quantity and voltage (v) over the series connection represents the second quantity. 
     
     
         12 . A method according to  claim 2 , wherein, for at least a part of a time, current (i) through the series connection of PV power sources represents the first quantity and voltage (v) over the series connection represents the second quantity, and, for another part of the time, the voltage (v) over the series connection of PV power sources represents the first quantity and the current (i) through the series connection represents the second quantity. 
     
     
         13 . An apparatus according to  claim 6 , in combination with:
 means for controlling the first quantity of the series connection; and   means for determining values for the first quantity and the second quantity.   
     
     
         14 . An apparatus according to  claim 13 , in combination with an arrangement having a series connection of photovoltaic ((Pv) power sources.